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Title: Spin orientations of the spin-half Ir 4+ ions in Sr 3NiIrO 6, Sr 2IrO 4 and Na 2IrO 3: Density functional, perturbation theory and Madelung potential analyses

The spins of the low-spin Ir 4+ (S = 1/2, d 5) ions at the octahedral sites of the oxides Sr 3NiIrO 6, Sr 2IrO 4 and Na 2IrO 3 exhibit preferred orientations with respect to their IrO6 octahedra. We evaluated the magnetic anisotropies of these S = 1/2 ions on the basis of DFT calculations including spin-orbit coupling (SOC), and probed their origin by performing perturbation theory analyses with SOC as perturbation within the LS coupling scheme. The observed spin orientations of Sr 3NiIrO 6 and Sr 2IrO 4 are correctly predicted by DFT calculations, and are accounted for by the perturbation theory analysis. As for the spin orientation of Na 2IrO 3, both experimental studies and DFT calculations have not been unequivocal. Our analysis reveals that the Ir 4+ spin orientation of Na 2IrO 3 should have nonzero components along the c- and a-axes directions. The spin orientations determined by DFT calculations are sensitive to the accuracy of the crystal structures employed, which is explained by perturbation theory analyses when interactions between adjacent Ir 4+ ions are taken into consideration. There are indications implying that the 5d electrons of Na 2IrO 3 are less strongly localized compared withmore » those of Sr 3NiIrO 6 and Sr 2IrO 4. This implication was confirmed by showing that the Madelung potentials of the Ir 4+ ions are less negative in Na 2IrO 3 than in Sr 3NiIrO 6, Sr 2IrO 4. Most transition-metal S = 1/2 ions do have magnetic anisotropies because the SOC induces interactions among their crystal-field split d-states, and the associated mixing of the states modifies only the orbital parts of the states. This finding cannot be mimicked by a spin Hamiltonian because this model Hamiltonian lacks the orbital degree of freedom, thereby leading to the spin-half syndrome. As a result, the spin-orbital entanglement for the 5d spin-half ions Ir 4+ is not as strong as has been assumed lately.« less
 [1] ;  [2] ;  [3] ;  [1]
  1. North Carolina State Univ., Raleigh, NC (United States)
  2. Fudan Univ., Shanghai (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China)
  3. Max Planck Inst. fur Festkorperforschung, Stuttgart (Germany)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 144; Journal Issue: 11; Journal ID: ISSN 0021-9606
American Institute of Physics (AIP)
Research Org:
North Carolina State Univ., Raleigh, NC (United States)
Sponsoring Org:
USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR) (SC-21)
Country of Publication:
United States
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; magnetic anisotropy; spin-half ions; spin-orbit coupling; Madelung potential
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1242560